Method of incorporating polychloroprene in paper



Patented Nov. 3, 1953 UNITED STATES PATENT "OFFICE "mil ion or ingiirzmrmlerory- Robert H. walsh, woodstown, N. Jr, and William .W. Pockn1an, Wilmington, l)el.-, assignors to I du Pont de Nemours & Company, Williiiiig'ton, DeL, a corporation of Delaware 'Nc'nrawing. Application November-'27, 1-948,

Serial No. 62,414

H 1 Claim.

T-hisinvention'relates to the after paper making, more-particularly to method of incorre-t ns rape rubberli q yci s h rp -1,3-butadiene, hereinafter referred to aspolychloroprene and'usu'ally referred to in the trade rn p V Because for its poor jphysical properties, the use of paper has been limited as an engineering raw material, but considerable work has been undertaken to improve its physical properties. The addition of melamineste irnprove the wet tensile strength of thepaper widely known and old in the art. The'addition of waifesjto improve water and grease resistance is also old. Ihe addition of urea formaldehyde resinshas been used to increase the tensile strengthand plasticizers of the glycerin, 'tri crimyl phosphate and diocetyl sebaeate class have been used also over a relatively long period of tirne as additives to increase the elongation properties of paper products. While these additions result in a marked increase in one physical property, they usually cause a depreciation of some other property. For instance, the addition of dioctyl sebacate to paper increases its elongation but decreases its tensile strength, etc. e 7

The treatment of paper with polych-loroprene.

however, has been found to cause a, worthwhile improvement in all the essential physical prop erties, such as tensile strength-, elongation, fold resistance andtear strength. 'Ihistreatment is now most widely carried out saturation probesseswhich consist of the application of an aqueous dispersion of Y the polychloroprene as a separate step after the formation of the paper. It

would be much simpler and, hence, much cheaper to incorporate the polychloreprene inte the paper pulp (in the manner in which coloring matter and fillers are incorporated) before its formation into paper, thus having the steps of separately H impregnating the paper with the polychloroprene, and then drying the paper for a second time. However, it has been found that, when negatively charged polychloroprene latices of the usual type are mixed with anaqueous suspension of paper pulp, little or no combination with the fibers takes place and, even wh'en a eoagulant such as aluminum sulfate is adde'd, the elasto'n er particles are deposited on the paper fibersin an extremely non-uniform manner. Suchpaper has poor formation, varying greatly tensile strength from one part of the sheet to the ether, and is often inferior to the paper separately treated with the polymer dispersion after preparation;

l mv d..1re tsa eicb ined y r i a 925 tively charged dispersion with the negatively charged paper fibers, but this does not offer "a practical solution of the problem because of the cost'of these pe'sitively charge dispersions and thediflicul'tie's "entailed in adding them to the Dull Ari object of this invention is to produce'paper of imme se-physical properties by treating the pulp with polychloroprene dispersions before the formation of pap'crshects. Afinore'spcifi'c object of the present invention is to deposit polychloropre'ne from an aqueous negatively charged dispersion uniformly upen paper fibers suspended in water. A further object "is to improve the rhethc'd jb'f treating paper" {pulp with dispersions of polychloroprene to preduce paper havin imprqvee general prcpertres, being uniform in strength and other physical preps-rues. other objects and advantages or the intention will appear Iron: the folldwing desc1"ipti'en.

These cb'ject's 'cr thi's invehtien are attained by adjusting thediirrence between the electrical charge en the pulp-fibers and the electrical charge on the polychloroprehe latex particles (as indi--- hated by read-mes obtained with a glass electrode) before ini'xiiig'to less than 5'0 millivolts, then mixing the two dispersions, adding a coagulant, and forming paper. g

The ad ustment of the particle charge may be brought about either by making the charge on the paper pulp fibers iricre negative or by makmg the "charge on the latex particles less negative, er by a combination of both operations. In other words, it has been found that the poor results elatain'ed on mixing the olychlcrcprene disp'ei-- siohs with the di persed aper filters is due to the disparity between their respective electrical charges, the foifzhcr usually havmg charges ofth'e order 25?) nfi'illivolts, while the charge on the latter-is iisi alry about -2'5.

Methods er increasing the negatii're charge on the ,pulp particles by adding materials such as alkali, sodium silicate, or sodium rosinate, are usually less desirable than methods of decreasing the charge on the latex particles, since the pulp is usually present in the larger amc'u tand 'a'd justlnent of its charge frequently leads {t5 the presence of undesirably large amounts of elec: trolytes in the finished paper. Themethod of reducing the strongly negative charge on the later; particle, although it is the preierred method of carrying out the inyentiodreduires a certain am n c jca n rde iob jl c' f ult The reduction in the charge on the latex particle is usually brought about through the addition of electrolytes, particularly salts of polyvalent metals such as aluminum sulfate, or by adding acids. Such additions tend to destablize the latex and frequently even lead to precoagulation, making the latex mix unsuitable for further operations. These difficulties may be overcome by the addition of dispersing agents often called dispersion stabilizers, and by diluting the latex before adding the electrolyte or by a combination of both processes. The extent of the dilution and the amount of the stabilizing agents to be added depends on the nature and concentration of the electrolyte being added and on the extent to which the charge is to be altered. This invention is particularly directed to the use of negatively charged polychloroprene latices in which the particle charge is more negative than 100.

The following examples are given to more fully illustrate the invention. In these examples the parts designated are by weight, unless otherwise specified.

Example 1 A polychloroprene dispersion was made by dissolving 32 parts of ester gum, 7.92 parts of wood rosin and 0.1 part of iodoform in 100 parts of chloroprene, and, after dispersing this solution in 140 parts of water containing 0.8 part of potassium persulfate and 1.67 parts of sodium hydroxide, polymerization was carried to substantial completion at 40 C.

One hundred (100) parts by weight of this dispersion of polychloroprene and ester gum containing approximately 50% solids was diluted with 410 parts of water and the dispersion was then stabilized with 50 parts of a solution of the sodium salts of the dinaphthylmethane sulfonic acids made according to U. S. Patent 1,336,- 759. Finally, 30 parts of a 5% aluminum sulfate solution first diluted with 410 parts of water were added rapidly with stirring. This treated latex (in which no coagulation had taken place because of the presence of the stabilizer) was then added to 50 parts (dry basis) of bleached sulfite pulp of 400 Canadian Freeness dispersed in 2000 parts of water in a paper beater. Sufficient additional water was added to insure good circulation. The stock was circulated for aboutlO minutes. Aluminum sulfate (equivalent to 100 pounds per 1000 pounds of dry pulp) was added, and precipitation of the latex upon the pulp occurred in a very short period of time. The stock was diluted to 0.5% concentration, and sheets .005 inch thick were formed in the usual manner and dried at 180 F. These sheets (identified as A in the following table) were perfect in formation and had excellent physical properties. They are compared below with sheets similarly made with latex which had not been treated to adjust the particle charge (designated B), and also with sheets made without latex from the same pulp (designated C).

1 Tensile strength in pounds of a 1 inch strip of paper 0.005 inch in thickness.

It will be seen from this table that, although the use of untreated polychloroprene latex (B) gives paper which at some places is considerably stronger than when no latex is used, the strength of sheets varies widely and at other places are very much weaker than the control (C). On the other hand, when the latex treated according to the present invention is used (A), the tensile strength is very uniform and much higher than that of either the control or the best of the paper made with the untreated latex.

Another advantage of the treated polychloroprene latex is the rapidity with which it is completely exhausted onto the fibers. Weight determinations show that only 92% of the latex solids were absorbed from the untreated latex, while 100% absorption was obtained with the treated material. This was confirmed by the observation that the back water (water remaining after paper is formed) was clear.

The amount of aluminum sulfate to be added to the polychloroprene latex for sensitization purposes in the above example was determined as follows: A 100 gram sample of the 50% latex used therein was diluted with 850 cc. of water, treated with 50 cc. of a 10% solution of the salt of the dinaphthylmethane sulfonic acid, and then electrometrically titrated with a 5% aluminum sulfate solution, using a Beckman pH meter with a glass electrode. The aluminum sulfate solution was added in small increments with eflicient stirring and a reading, directly in millivolts, was taken after each addition. The original reading was -250. When the reading was the same as that previously determined for a suspension of the sulfite pulp used, which in this example was 25 millivolts, the total amount of aluminum sulfate solution added was recorded and the amount required to treat the amount of latex used on the example was calculated by proportion. Although some variation in this amount of aluminum sulfate is allowable, it has been found that satisfactory results are not obtained unless the amount corresponds to a reading within 50 millivolts of that of the pulp.

Example 2 Seventy-five parts of the polychloroprene latex used in Example 1 was treated with stabilizing agents and aluminum sulfate in the same manner and in the same proportions as described therein, and was then added to 50 parts (dry basis) of pulp suspended in water as in that example. After circulating this mixture in the beater for 10 minutes, 25 additional parts of the 50% latex, first diluted to a 5% concentration, was added. This caused uniform precipitation of the entire system in 10 to 20 seconds without further use of aluminum sulfate. Sheets formed as before had a range of tensile strength of from 48 to 53 pounds. This procedure has the advantage of using much less aluminum sulfate and hence reducing the brittleness or tinniness" of the sheets.

Similar results were obtained using other types of polychloroprene latices in the procedures of either Example 1 or Example 2. These include latices like that used in Example 1 but containing no ester gum and made with only 4 parts of rosin and parts of water, and latices made by polymerizing chloroprene in the presence of from 0 to,2% of sulfur in an alkaline sodium rosinate emulsion. These procedures were further varied by stopping the polymerization when only part of the chloroprene has been polymerized and removing the unchanged portion. Those lat ices containing the softer polymers, for example, those made with iodoform or larger amounts of sulfur or ester gum, or those in which the polyhesitation; was started haters c9mh1shep...eete

raises a e ter see paper at hi her ens le trength are here- M4 tore, preferred where st en th s; a seasid Ename s emition' use of mg (If Gne hundred (100% parts of bleached sulfite polymer; latex ISzllLllfifiEfi Ed. the 1 K? example. Q, m 'g Freeness. 400 in 200 parts of Example water were treated with parts of polychloroprene in the form ofa diluted latex with adjusted Gne hundred (000)- parts (dry basis) of particle charge. The latter was made up bybleached Kraft pulp, beaten to a Ganadian Freetreating 20 parts of the 50% latex used in Exness of; 51 was treated in 2000 P ts or water ample 1 with 10 parts or a 10% solution r the h 19 0f p y hl pr in h o m o sodium sulfonate dispersion stabilizer used in its diluted latex, halfbeing added after ad- Example 11, dil ti to 5%, and then adding a, lus g its pa ti har with alum mnn u-I quantity of 2 .5% aluminum sulfate solution, de fate as inthe preceding e a p and h W htermined as described in Example '1 to adjust the out such treatment, the mixture of the two types latexparticles charge to approximately the same oflatex err-precipita in ch her, as in Excharge a the pul fibers; Before the addition or amp T la x mp yed; W s-made by polys this later; to the pulp, the latter was compounded merizing' chloroprene in the presence of 5% dowith of zinc oxide and 2% of 2,5-d-itertiary d yl mercaptan While dispersed n n q l butyl hydroquinone (based on the weight of poly-- W t of n aqueous alkaline 4 sodium rosin-1 29 chloroprene). The mixture was then coagulated ate solution. Two (2-) parts of this 50% later:- with aluminum sulfate as in Example 1, and were diluted with waterto 5%, mixed with fprlped into sheets. For a comparison of the im.. parts of a 10% solution of the sodium sulfonate proved properties of the resulting paper, a secdispersion stabilizer used in Example 1 and 10 one product using natural rubber was prepared parts of a 2.5% aluminum sultate solution, and as follows: then added to the dilute pulp suspension as in One hundred (100) parts of paper pulp (dry Example 2. Coagulation was then brought about basis) from the same lot, to which had been y addi t ot pa ts f the 50% lat x. added 2% sulfur, 0.5% of the piperidine salt of likewise diluted to 5%. Sheets of paper were pentamethylene dithiooarbamate and 0.5% 01 formed as in the preceding examples. At the butyraldehyde-aniline condensation product, same time, portions of the same lot of pulp were based on the rubber, was treated with 16.7 parts treated with larger amounts of polychloroprene of a 60% centrifuged rubber latex containing in amounts up to 100% (polychloroprenesolids) 10 parts of natural rubber. Sheets were made as shown in the following table (using the profrom this and from the pulp without any added ceclure described above), and formed into sheets. material, as described in Example 1. The properties of" the resulting paper were as follows: F M 15mm 0 .V Parts polychloro-v Tensile Elon: ig g g 4 Tur-pem Poly.

39 h 100 of ggeg g a: gg gg i-lvlllgugug m%g l l fig. ubber 00mm 4 e l sih R-Wi .h 3 2, 3'6 5 3. 0 Elongatipn (percent) 3. 5 3. 5 '2 41 5 10,0 WtstreugthGbsJinch Width). 28 18 6 0.- r 00- Ternsehs ssetaq use oe s a 0 54 615 3,300 60.0 Flame res ance (inches not con- 53 7 4,300 180.0 summit"; 2,5 0 0 9 450 370. 0 Tensile strength after 14 days stor- I 10 7,000 1,200.0 age at C. (lbs./in. \vidth) 35 12 0 51 12. 8;.500 b. 00

Th t s, em l y d: in. hese examp es 0 1d wh re h ehq t his q rfi aiieh were carried out in accordance with the methods decr ed n TAPPI St ndards pu lish d y th 'l-fe hni l A ia n Qt t ev Eula ha Paper I d yhs e t s s eneral seps ed oi the following:

F res s nce orf d nduranss s d tsrmhied n t T- p t r. h e the samele ef pape und r 1 ki g am lead i fielded lter a e y i pp te r t on un il br a n Q-Qeu see TAPPI T423 M45.

Turpentine number is the number of seconds requi o tu pent ne. or d w th. a are o soak; through the sheet of paper under test. This is a measure of the permeability of'the paper to fats and oils. See TAPPI Ti54 M144:-

Flame resistance s determi d by a p ing a flam f r ten se ends o n en at a tee ineh strip of paper held horizontally in a frame and noting the length of the. strip, it any, remaining unburnt. See TAPPI- T461 M,

The Mullen value for burstingstren th is determined by clamping the paper over a flat. disc capable. of being distended by fluid pressure 3 .9-- plied to one side and noting the fluid pressure This example illustrates the adjustment of the charge of the pulp. fibers instead of that of the latex. Fifty (5,0). arts. o bl ache sulilts pulp like that. used n Exam l l wa dis e sed in 2000 parts of water and treated with ammo,- nium hydroxide to br n the read n n mi l valt to, 125. h s w s h m xed w th pa or the 50% p lychlorop sn late d EX.- ample 1 after first diluting it with {$50 parts of water. peas-ela ion wi h. lum num ulfate and ermation of she s earned o as 1 xam l v 1 ave a s m arl mhre Prod ct.

The present invention is applicable to all; types of paper pulp (deciduous or coniferous sulfite or mechanical, Kraft, rag, etc). The freeness (dewe at hyd ation. m b v ried er a var-y w d an e ulps fr 5 t 8 on nadian sha e havin be n ed s cc ul y- T-he rati at Pa e t sla t m may be arie o a wid rang d cl de a at s e pr c ical. r ms in t e art xam le. 3 i usa es h use of t .0 of latex sol ds based on the weight of the pulp. One per cent and ev n up. o 2 0% obvi us y m y be rs srated s xa t y th s m wa with anal ease results Il s smaller per entage are 1 s:

ally used for such effects as improved retention of fillers, pitch control, avoidance of two-sidedness, better utilization of colors and where moderate improvement in physical properties are desired, while larger amounts are used when a radical improvement or change in the physical or chemical properties, such as oil resistance, etc., is sought.

In temporarily stabilizing the latices against the coagulating action of the electrolytes added to reduce the particle charge, any of the recognized dispersing agents of the anionic, non-ionic or amphoteric types may be used. We have found the sulfonate type, such as the sodium salts of the sulfonated dinaphthylmethanes used in the above examples and the lignin sodium sulfonates, are very satisfactory. Ten per cent (10%) of these agents, based on the weight of the polychloroprene employed, is usually sufficient to prevent coagulation when normal amounts of sensitizing electrolytes are used. More may be necessary when less effective stabilizers or unusually large amounts of electrolytes are involved. The technique of stabilizing latices against coagulation is well known to those skilled in the art and does not form a part of the present invention.

The latex solids concentration at the time the charge is adjusted should be preferably not above 10% if ordinary amounts of dispersing agents are employed. From a practical standpoint dilutions under 4% are not desired, although completely operable. With the non-ionic dispersion stabilizers or where the use of larger amounts of stabilizers is not otherwise detrimental in the finished product, latex concentrations up to 30% are entirely practical.

The latices may be compounded with various compounding ingredients such as fillers, colors, softeners, vulcanization aids, antioxidants and the like. Thus, zinc oxide and an antioxidant such as phenyl beta-naphthylamine are very generally added. The compounding ingredients may be first incorporated into the latex, but it is often convenient and equally satisfactory to add them I separately to the pulp.

The latex can be added to the pulp at any point in the system prior to formation of the sheet, and while the examples given above refer specifically to addition at the beater, the present invention is applicable if the latex is added to the pulp after discharge from the beater, after passing through the Jordan or hydrating machinery or at the head box or at any point prior to coagulation of the pulp.

The coagulation of the mixture of pulp and latex may be brought about in many different ways. A preferred method is the addition of aluminum sulfate, as illustrated in the examples.

Other electrolytes, particularly those giving polyvalent ions, may also be used, such as calcium chloride, magnesium sulfate, barium chloride and thorium chloride. A mixture of aluminum sulfate and calcium chloride has been found particularly useful when there is a tendency for the sheet to stick to the screen. Acids may also be used, either alone or in combination with salts, for example, sulfuric, hydrochloric, formic and hydroxy acetic, as the sheet tends to be softer when an acid is used. The quantity of electrolyte used in the final precipitation or coagulation of the pulp and latex combined should be enough to give complete coagulation and is determined as in ordinary papermaking. Coagulants which are inactive at ordinary temperatures but are activated by warming, such as 2-nitropropane, may be employed. As illustrated in Example 2, the untreated latex with high particle charge may be employed as the coagulant. Here the portion of the latex reserved to act as the coagulant should be between 5% and 50% of the total. The mixture of pulp and latex particles with adjusted particle charge may also be coagulated in a similar manner by adding a positively charged latex. Both methods of coagulation involving the addition of a second latex have the advantage of reducing the brittleness and tinniness caused by aluminum sulfate or other electrolytes.

In addition to the advantages of this invention illustrated above, the present invention largely eliminates two serious difficulties in the paper-making art, namely, the accumulation of pitch from sulfite pulp on both the metallic and non-metallic parts of paper-making equiment, and the phenomenon in colored paper known as two-sidedness.

The presence of pitch results in loss of production time, due to clogging of the wires and felts which results in slower drainage rate, and gives paper containing lumps or aggregates of pitchy material dispersed throughout the sheet.

Sulfite pulp normally contains from 0.8% to 5% pitch. Authorities believe that if the pitch content in pulp is above 1%, difiiculties in operation will be experienced in the plant. When paper pulp is treated with even small percentages of polychloroprene latex according to the present invention, it is found that apparently all the pitch becomes uniformly and finely distributed throughout the paper in such a manner that it does not alter the properties of the paper to any appreciable extent. Thus the pitch, instead of building up in concentration in the back water and then precipitating in massive form as objectionable lumps in the apparatus and on the paper, is rendered unobjectionable when operating the process of the present invention.

Two-sidedness in colored paper is caused at least in part by the unequal absorption of the dye by the various types and sizes of fibers present in the pulp. These kinds of fiber are partly separated during the formation of the paper sheet, with the result that their relative proportions on the two sides are different. If they have an unequal affinity for the dye, the two sides will therefore differ in the strength of the color. It has been found that, when the present invention is used, the dye is more uniformly absorbed by all types of fibers, resulting in a sheet in which the two-sidedness is eliminated or largely reduced. In addition, the same amount of dye used in connection with the present invention gives a substantially stronger color than otherwise.

Other important advantages secured by the use of the present invention relate to the incorporation of large amounts of fillers into the paper. The addition to the paper pulp of fillers such as calcium carbonate or clay results in a cheaper sheet having a better printing surface, although one which has decreased elongation and strength (as measured by the various tear and rupture tests), particularly when large "amounts are used. Large amounts of such fillers added to the pulp are, furthermore, only very incompletely retained in the sheet and there is a definite upperlimit (about 30%) above which amidst 92 the filler is no longer retained by the fibers. However, whenv even. small proportions. at poly.- chloroprene: are incorporated, large proportions of fillers may be incorporated; without seriously impairing the physical properties, of the paper, and the percentage of filler retained in the sheet is much increased. These effects are illustrated by" the fol-lowing examples.

Into a mixedpulpconsisting of 68 parts of ground wood and 2.4 parts of. bleached sulfite pulp, there was incorporated varying amounts oi calcium carbonate as given in. the following tables, then 2% of polychloroprene in the fprm of the sensitized latex made in Example I" was added, and finally, the mixture was coagulated with aluminum sulfate. Sheets were then formed, analyzed and tested in comparison with sheets made from the same stock without added polychloroprene. The amount of calcium carbonate and polychloroprene added is based on the weight of the wood and pulp mixture (dry basis).

It will be seen from this that the sheets containing polychloroprene are stronger in all cases, particularly when large amounts of filler are used. Sixty per cent (60%) of added calcium carbonate with polychloroprene lowered the strength no more than did only 25% of added calcium carbonate without polychloroprene.

Percent of calcium carbonate retained (based on amount added) Calcium carbonate added, percent Without The above figures for per cent of calcium carlbonate retained were calculated from ash determination upon the paper. They show that a much larger proportion of the added filler is retained in the paper when polychloroprene is present and that accordingly a larger percentage, based on the pulp, may be incorporated than is possible otherwise.

Apparently related to the improved retention of fillers is the more complete retention of the fines or smallest fibers contained in the pulp. The normal efliuent from the paper-making operation when the present invention is used is freer from suspended matter and hence presents a much less serious disposal problem. Also contributing to the clarity of the efliuent is the complete exhaustion of the latex upon the fibers (as discussed in connection with Example 1), when the method of the present invention is used. Even though these fine particles are retained in the sheet, the rate of drainage is unusually high,

10 and hencetire-paper-making operation may be carried out at increased speed.

A. further advantage of. the present invention is the, possibility of Jord'aning the pulps after adding the latex. The improvement in. the physical properties of the paper. brought. about by the use of. the present invention is of: particular valuein connection with. paper made from inferior pu lps. One ofthe problems of the paper industry'atthis time is the shortage of desirable pulp. The normal stocks of hemlock and spruce have become seriously depleted; and the use of oak..l oplar', yellow birch, etc., i s now a necessity if" the paper industry is to continue supplying their large demand. These pulps lack in strength and the usual aper qualities normally associated with paper produced from hemlock and spruce. For instance, it has been claimed that paper produced from poplar is approximately from 25% to 40% poorer in physical properties (tensile strength, Mullen, Elmendorf and edge tear) than a similar bleached spruce. Where the printing industry and other industries using paper have have set their manufacturing operations to use a paper of certain quality and physical characteristics, they will not be able to handle paper of a lower grade especially when the difference between the two types of papers is great. Therefore, it becomes apparent that a marked improvement in the physical properties of paper prepared, for example, from poplar, must be obtained. The addition of a very small amount of polychloroprene, i. e., 2%, from the latex used in Example 3, for instance, improves the properties of the paper so as to make it of the desired class at a very low cost.

While the invention has been illustrated using polychloroprene itself, other polychloroprene elastomers containing a minor amount of copolymerizable compounds may be employed in the same manner and are included in the expression polychloroprene elastomers, since they have the general characteristics of polychloroprene itself.

We claim:

In the process of incorporating a polychloroprene elastomer latex, in which the particle charge is more negative than millivolts, into an aqueous suspension of a cellulose paper pulp in which the dispersed paper fibers carry a negative charge for modifying the physical characteristics of the paper to be prepared therefrom, the steps which comprise diluting the latex to a solidsconcentration of from 4% to 10%, stabilizing the latex by the addition of the sodium salt of a sulfonated dinaphthylmethane thereto and adding aluminum sulfate in an amount suificient to bring the electrical charge on the polychloroprene elastomer latex particles to Within 50 millivolts of the charge on the paper pulp fibers, adding the polychloroprene elastomer latex to the aqueous dispersion of the cellulose paper pulp, coagulating the mixed dispersion, and forming a paper sheet therefrom.

ROBERT H. WALSH. WILLIAM W. POCKMAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,567,646 Hopkinson et al. Dec. 29, 1925 1,621,399 De Cew Mar. 15, 1927 1,799,217 De Cew Apr. 7, 1931 (Other references on following page) 1 1' UNITED STATES PATENTS Number Name Date Rose et a1 Feb. 2, 1932 Carnie Feb. 9, 1932 Tucker Feb. 26, 1935 Faldini Oct. 15, 1935 Johnson Sept. 24, 1940 Merrill Oct. 13, 1942 Scott Sept. 21, 1943 Young Feb. 1, 1944 Smith Feb. 29, 1944 Pretzel May 8, 1945 Pretzel May 8, 1945 Number Name nate Tausch May 28, 1946 Bebb Jan. 13, 1949 Johnson May 10, 1949 FOREIGN PATENTS Country Date Great Britain June 30, 1932 OTHER REFERENCES Stanton et 211., Paper Trade Jour., vol. 123, No. 6 (pp. 48-52).

Partridge, India, Rubber World, May 1948, pp. 

